We don’t write much about the fungal microbiome on this blog, but it may be every bit as important as the bacterial microbiome (and let’s not forget about the archaeal and eukaryotic microbiomes, and virome as well!). Fungi are not as abundant in the microbiome as bacteria, which is probably why they are not as heavily researched, but they are known to cause diseases. For example, vaginal yeast infections and oral thrush are caused by fungi belonging to the Candida genus.
We recently wrote about a study that linked bacterial biofilm formation with colorectal cancer. In this blog we mentioned that colorectal cancer is likely to have environmental causes. Researchers from China hypothesized that fungi may be one of these risk factors, so they conducted an experiment to find out. They recently published their results in Nature Scientific Reports.
The researchers first sampled the microbiomes of 27 patients with various stages of colorectal tumors, in addition to other, healthy areas of those patients’ guts adjacent to the tumors. They then sequenced the genomes of the samples to determine which fungi existed, and where. They discovered that fungal diversity was lower on tumors compared to other areas of the colon. In addition, two known pathogenic fungi, Candida and Phoma existed in higher levels on tumors compared to the adjacent areas. Finally, they found distinct differences between individuals with advanced and non-advanced tumors. Those with advanced tumors had a higher abundance of two other known pathogenic fungi, Fusarium, which has been associated with intestinal disease in the past, and Trichoderma, which has been associated with infections of various organs.
This study did not involve any healthy patient controls, and its sample size was somewhat limited. Still, the results are intriguing because gut fungi that are known to cause inflammation elsewhere in the body are being found at the site of tumors. Even if these fungi are not causing the tumors, they could at least be potentially used as a diagnostic or biomarker for tumors. While we know that some fungi can be dangerous, we note that even specific genera are not always pathogenic, and sometimes they can exist normally in a host and only turn pathogenic at a later time. Like other aspects of the microbiome, the story is complicated, but we would be willing to bet there is at least one beneficial fungus among us.